Tensioning device for traction means

ABSTRACT

A tensioning device for traction means, especially for toothed belts, is provided with a tensioning arm ( 3 ) on which a tensioning roller ( 1 ) is rotatably arranged. Furthermore a stopper ( 12 ) is provided which restricts a swiveling angle of the tensioning arm ( 3 ), whereby a detachable locking device ( 15 ) is provided through which the tensioning arm ( 30 ) and the stopper ( 12 ) are locked for joint swiveling into a position provided for the stopper ( 12 ).

BACKGROUND

1. Field of the Invention

The present invention concerns a tensioning device for traction means,especially toothed belts, as they are used, for example, in toothed beltdrives of motor vehicles. The present invention furthermore concerns aprocess for installation of, in particular, a prestressed tensioningdevice for traction means.

2. Description of Related Art

From U.S. Pat. No. 4,832,665, for example, a tensioning device fortoothed belts is known where a tensioning roller is pivoted on aneccentric. The eccentric is arranged pivotably on a carrier which isflange-mounted on a motor by means of a screw. A spiral spring arrangedon the eccentric is supported on the one hand on the motor and on theother on the eccentric such that the eccentric with the tensioningroller is sprung against the toothed belt. With this tensioning device,a locking pin is provided which keeps the tension spring in aprestressed arrangement prior to starting up. After flange-mounting thetensioning device to the motor, the locking pin is withdrawn so that theeccentric is sprung under the force of the tension spring against thetoothed belt. The toothed belt can wind around the toothed drive pulleysof the crank shaft and the camshafts. It is important that a jumping ofthe toothed belt over the teeth of the toothed drive pulleys isprevented, since otherwise the control times are altered in anundesirable manner so that a total failure of the internal combustionmachine can result. In order to avoid a jumping of the toothed belt,with the tensioning device in accordance with U.S. Pat. No. 4,832,665, afreewheel is arranged between the bolt mentioned and the eccentric. Whenin the strand of the toothed belt, with which the tensioning rollerinteracts, excessively high strand tension arises, the eccentric isswivelled against the force of the tension spring. The grip rollerfreewheel engages in this direction so that an undesirably highdeflection of the eccentric out of the belt drive is prevented. As soonas excessively high strand tension has built up, the tensioning rollerexerts spring force against the toothed belt so that the requiredtension is maintained in the strand. In this way, a jumping of thetoothed belt is avoided. The freewheel accordingly here takes over thefunction of a stopper which restricts the swivelling angle of thetensioning arm. With this tensioning device, the expensive constructionof the stopper is nonetheless disadvantageous, which requires thefreewheel as well as a damping fluid in order to make possible adeflection of the eccentric out of the belt drive.

A so-called double eccentric tensioner is known from DE 40 15 028 A1which includes an adjusting eccentric and a working eccentric. Duringinstallation on the motor block, the tensioning device is at firstloosely screwed with bolts passed through an eccentrically arrangedfastening bore hole. The tensioning device is swung against the beltwith an adjusting tool inserted into a hexagonal recess. When this isstressed, a reaction force acts upon the tensioning device. With furtherswivelling, the spiral spring is stressed and the installation toolswivelled. The swivelling process is continued until notches provided onthe flange and a plastic disk are covered. In this situation, aprojection is situated in the middle of a recess of the swivelling areaof the tensioning arm. The bolt is screwed fast in this presetting.These double eccentric strainers have the disadvantage that when theadjusting eccentric is swivelled too far for the presetting, the onenotch wanders past the other notch. If now the adjusting eccentric isswivelled back until the two notches are aligned with each other, theprojection is no longer situated in the center of the recess mentioned,but rather somewhat displaced from it. The reason for this displacementis an internal friction which arises between the machine parts duringpresetting. In this case, the stopper which is formed by the projectionand the recess, has another position so that the swivelling region ofthe tensioning arm is altered. A hysteresis effect takes place. Inpractice, this can lead to considerable problems, since first strandtension forces deviate from their predetermined values and secondlybecause the swivelling range is no longer adjusted to the behavior ofthe traction means drive.

SUMMARY

The object of the present invention is therefore to provide a tensioningdevice which is simply constructed and the starting of which is reliablypossible.

With the invention, a tensioning device for traction means, especially atoothed belt, is proposed which is provided with a tensioning arm onwhich a tensioning roller is rotably arranged, and which is furthermoreprovided with a stopper which restricts a pivoting angle of thetensioning arm, whereby a detachable locking device is provided by whichthe tensioning arm and the stopper are locked into a position providedfor the stopper for joint swiveling.

With the tensioning device of the invention, additional machineelements, as for example free wheels, can be dispensed with.Furthermore, it is assured that any friction possibly arising betweenparts to be adjusted has no influence on the trouble-free position ofthe stopper, because due to the locking, no relative motion betweentensioning arm and stopper takes place during installation. If thetensioning device is installed in a toothed belt drive, a tension springcan press the tensioning arm against the toothed belt, whereby thetensioning arm swivels together with the stopper. This swiveling motionends when an equilibrium of forces between strand tension, the force offriction and tension spring force is established. In this situation, thestopper is fixed, and the locking described is relieved so that afurther operation-conditioned swiveling of the tensioning arm takesplace independently of the stopper. The position of the stopper is nowcoordinated with the toothed belt drive. Faulty adjustments, especiallydue to the hysteresis effect, are ruled out because the stopper is onlyswivelled in the direction of the belt, and because the stopper is movedtogether with the tensioning arm.

The tensioning arm and the stopper can both be provided in any givencase with at least one arrangement which are provided for strikingagainst each other, whereby the arrangements are set at a distance fromeach other if the tensioning arm and the stopper are locked with eachother. This distance is precisely dimensioned such that after installingthe tensioning device, the swiveling angle of the tensioning arm isbrought out of its middle position (which at least generally agrees withthe position after concluding installation) and against the tensioningforce of the tension spring on the toothed belt drive. If the excessivestrand tension causes a strong deflection of the tensioning arm againstthe spring force of the tension spring as a consequence, this deflectionis stopped in time by the stopper or by the striking of the arrangementson each other. As soon as the strand tension has diminished, thetensioning arm immediately springs under the spring force of the tensionspring against the toothed belt so that a jumping of the toothed belt isreliably prevented.

An especially simple and economical tensioning device provides that thetensioning arm is pivotably located on a carrier, whereby a tensionspring is supported on the one side on the carrier and on the other onthe tensioning arm. This arrangement makes a prestressing of the tensionspring possible. If the tensioning arm, the stopper and the carrier arelockable with each other by means of the locking device, the followingadvantages result: First the locking can take place in an arrangement inwhich the tension spring is prestressed, and secondly a defined anglebetween stopper and tensioning arm can already be adjusted in advance.

An especially simple locking device provides a pin which engages forlocking in openings of the elements to be locked whereby the pin can bebrought out of engagement with the openings. In the simplest case, thetensioning arm, the stopper and the carrier can each be provided in anygiven case with holes which are aligned with each other, whereby the pinis passed through the holes. If the tensioning device in installed inthe toothed belt drive, the pin first merely needs to be withdrawn outof the carrier, the stopper is then fixed and finally the pin completelywithdrawn so that starting the tensioning device of the invention cantake place without further steps.

The carrier can include a base plate which is provided with a shaft onwhich the tensioning arm is pivoted. Such an arrangement is chieflyappropriate when the base plate is to be adapted to the contour of theflange surface of the motor. The shaft and the base plate are preferablyconnected fast with each other.

The already mentioned stopper can be formed in an especially simplemanner by a disk which is rotable in relation to the shaft. The capacityof the disk of being rotatable in relation to the shaft is necessary inorder to guarantee that the tensioning arm and the disk can only swiveltogether until the equilibrium of forces between strand tension andtension spring force is adjusted. After this, the disk can be fixedfriction-locking to the shaft.

With this arrangement, the tension spring can be formed by a helicaltension spring which is arranged on the shaft. The helical spring isthen supported on the one hand on the carrier and on the other on thetensioning arm constructed as an eccentric.

With a preferred refinement of the invention, the locking deviceprovides a pin which engages in openings of the disk and the eccentricand the carrier. With this tensioning device, the position of the diskin relation to the eccentric is established as a consequence of locking,whereby moreover the helical spring can be prestressed. For the helicalspring is on the one hand supported on the carrier and on the other handon the eccentric, and since these two elements are locked by means ofthe pin, the helical spring cannot relax.

The already mentioned fastening of the disk on the shaft preferablytakes place by means of a screw which engages into a hole providedthrough the shaft whereby the disk is pressed on the shaft and connectedfriction-locking with this when the screw is tightened.

This tensioning device can be advantageously refined in that the screwis passed through the hole executed as a central longitudinal hole andis screwed together with a frame-fast machine element, especially themotor block. Accordingly, this screw serves a double purpose, namelyfirst to fasten the tensioning device on the motor block and second tofasten the disk on the shaft.

The tensioning device described can be suited in an especially favorablemanner for the following process for placing the tensioning device intooperation. The tensioning device provided for this process describedbelow has the following features: A tensioning arm on which a tensioningroller is pivoted; a support on which the tension arm is pivotablylocated; a tension spring which on the one hand is supported on thecarrier and on the other on the tensioning arm; a stopper whichrestricts the swiveling angle of the tensioning arm; a detachablelocking device by means of which the tensioning arm and the support andthe stopper can be locked with each other. The process provides thefollowing steps: locking the tensioning arm and the carrier with eachother in an arrangement in which the tension spring is prestressed. Thisthus preassembled tensioning facility is incorporated in the tractionmeans drive, and the belt is laid on the tensioning roller. After this,the locking described is partially relieved such that only the stopperand the tensioning arm remain locked by means of the locking device,whereby the tensioning arm is sprung together with the stopper againstthe traction means under the force of the prestressed tension spring.Now the stopper is fastened. Subsequent to this, the locking iscompletely relieved so that the tensioning arm is pivotable relative tothe stopper. The stopper now has an optimal position. The swivelingangle of the tensioning arm up to catching on the stopper now presentis, on the basis of its amount, approximately as large as with thepreassembled tensioning device. For with the preassembled tensioningdevice, this swiveling angle is established by the locking of tensioningarm and stopper with each other, whereby the stopper is fixed followingjoint swiveling of tensioning arm and stopper.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail below on the basis of apreferred embodiment shown in the drawings, wherein:

FIG. 1 is a longitudinal section through the tensioning device of theinvention;

FIG. 2 is an elevational view of the tensioning device of FIG. 1 lookingtoward the left; and

FIG. 3 is an elevational view of the tensioning device from FIG. 1looking toward the right.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With the tensioning device of the invention according to FIG. 1, atensioning roller 1 is rotatably supported on a ball bearing 2 locatedon an eccentric 3. The eccentric 3 is pivoted on a support 4 through aninterposed sleeve bearing 5. The support 4 includes a cylindrical shaft6 and a base plate 7 which is arranged on one end of the shaft 6 and isjoined fast with this. The base plate 7 serves for installation and asan anti-rotation element of the tensioning device in relation to a motorblock (not shown) of an internal combustion engine.

Furthermore, a helical spring 8 is provided which on the one hand issupported on the base plate 7 and which on the other engages with theeccentric 3.

The shaft 6 is provided with a central longitudinal bore hole 9 throughwhich a screw 10 is passed. The screw 10 engages in its thread segment11 into a tapped hole of the motor block (not shown). On the other endof the bolt 6 a disk 12 is arranged rotatably on a ledge 13 of theshaft. The disk 12 projects generally axially so that it can be clampedbetween a screw head 14 of screw 10 and the shaft 6 when screw 10 istightened. The clamping brings it about that disk 12 is connectedfriction-locking with shaft 6.

Furthermore, a pin 15 is provided which locks the disk 12, the eccentric3 and the support 3 with one another. For this reason, the base plate 7of the support 4, the eccentric 3 and the disk 12 have in each case ahole 16, 17, 18 through which the pin 15 is passed. The helical spring 8is prestressed in the representation shown.

From FIG. 2, it can be inferred that base plate 7 has a fork-like end 19which is provided for engagement with a motor block (not shown).Furthermore, it is to be gathered from this representation that theeccentric 3 is provided with a raised projection 20 which at leastpartially overlaps with the disk 12 in an axial direction. The disk 12furthermore has a radially directed bar 21 which is provided with thebore hole 18 for the pin (which is not depicted in this representation).The bar 21 and the projection 20 each have an arrangement 22, 23 whichare provided for striking against each other. After starting thetensioning device of the invention, a swiveling of the eccentric 3 inthe direction of the stationary disk 12 is restricted by the striking ofarrangements 22, 23.

The shape of the base plate 7 is shown in FIG. 3.

The mode of action of the tensioning device of the invention will beexplained below. The described, preassembled and prestressed tensioningdevice is installed in the toothed belt drive whereby screw 12 istightened to such an extent that the disk 12 is still rotatable inrelation to shaft 6. Now the pin 15 is moved so far axially until it hasleft the bore hole 16 of the base plate 7. In this situation, theeccentric 3 is swivelled together with the disk 12 under the tensionforce of the helical spring 8 against the not represented toothed beltand pressed on this. After concluding this swiveling process, the screw10 is tightened fast, whereby the disk is clamped between the screw head14 and the bolt 6. Now the disk 12 is connected friction locking withthe shaft 6. Now the pin 15 is completely withdrawn, and the tensioningdevice of the invention is ready for operation.

Below the case is described where excessively high strand tension actson the tensioning roller. Under this strand tension, the eccentric isswivelled against the helical spring 8, thus out of the drive. Thisswivelling motion is, however, restricted in that finally the raisedprojection 20 with its arrangement strikes against the arrangement 23 ofdisk 12. A further swiveling of the eccentric 3 is not possible. Thisswiveling path is dimensioned such that a jumping of the toothed belt isruled out for if the excessive compressive forces are reduced, theeccentric can directly follow the toothed belt under the force ofhelical spring 8 so that no slippage can occur between toothed belt andtoothed belt disk.

Installation errors are ruled out with the start up described. Theposition of the disk 12 is unambiguously established. The advantagesdescribed likewise result with a modified embodiment of the inventionwhich is described below. With this modified embodiment, the disk 12 isconnected torsion-resistant with the shaft 6. The disk 12 and the shaft6 can also be joined with each other in one piece. In contrast, with themodified embodiment, the base plate 7 is rotatable in relation to shaft6.

With the tensioning device illustrated, the screw 10 can be providedwith a retaining ring on its free end which is supported on the screw onthe one hand and on the shaft 6 on the other. In this way, the screw isnot only held in the shaft safe against loss, but the axial force of thehelical spring 8 is introduced through this retaining ring into screw10.

Reference Numbers

1 Tensioning roller

2 Ball bearing

3 Eccentric

4 Support

5 Sleeve bearing

6 Shaft

7 Base plate

8 Helical spring

9 Longitudinal hole

10 Screw

11 Thread segment

12 Disk

13 Ledge

14 Screw head

15 Pin

16 Hole

17 Hole

18 Hole

20 Projection

21 Bar

22 Arrangement

23 Arrangement

What is claimed is:
 1. Tensioning device for traction means, comprisinga tensioning arm (3), on which a tensioning roller (1) is rotatablyarranged, and with a stopper (12) which restricts a swiveling angle ofthe tensioning arm (3), whereby a detachable locking device (15) isprovided by which the tensioning arm (3) and the stopper (12) are lockedtogether and are jointly swivelable into an adjustable installationposition for the stopper (12), wherein the tensioning arm (3) and thestopper (12) are each provided with at least one arrangement (22, 23)which are provided for striking against each other, whereby thearrangements (22, 23) of the tensioning arm (3) and stopper (12) are setat a preset distance from each other in a swiveling direction of thetensioning arm (3) in the installation position.
 2. Tensioning deviceaccording to claim 1, wherein the locking device includes a pin (15)which engages in openings (16, 17, 18) of elements to be locked, wherebythe pin (15) is disengageable from engagement with the openings (16, 17,18).
 3. Tensioning device according to claim 1, wherein a defined anglebetween the stopper and the tensioning arm in the installation positionis predefined.
 4. Tensioning device according to claim 1, wherein thetensioning arm (3) is pivotably arranged on a support (4), and a tensionspring (8) has one end supported on the support (4) and another endsupported on the tensioning arm (3).
 5. Tensioning device according toclaim 4, wherein the tensioning arm (3), the stopper (12) and thesupport (4) are lockable with one another by the locking device (15). 6.Tensioning device according to claim 4, wherein the support (4) includesa base plate (7) which is provided with a shaft (6) on which thetensioning arm (3) is pivotably arranged.
 7. Tensioning device accordingto claim 6, wherein the shaft (6) and the base plate (7) are fastenedtogether with each other.
 8. Tensioning device according to claim 7,wherein the stopper is formed by a disk (12) which, in a first state, isrotatable in relation to the shaft (6) and, in a second state, isattachable form-locking on the shaft (6).
 9. Tensioning device accordingto claim 8, wherein the tension spring is a helical spring (8) arrangedon the shaft (6) and is supported on one end on the support (4) and onthe other end on the tensioning arm which is constructed as an eccentric(3).
 10. Tensioning device according to claim 9, wherein the lockingdevice has a pin which engages in holes (16, 17, 18) of the disk (12),the eccentric (3) and the support (4).
 11. Tensioning device accordingto claim 9, wherein a screw (10) engages into a hole (9) provided in theshaft, whereby the disk (12) is pressed on the shaft (6) and connectedthereon upon the screw (10) being tightened.
 12. Tensioning deviceaccording to claim 11, wherein the screw (10) is passed through the holewhich is constructed as a central longitudinal hole (9) and is screwedto a frame-fast machine element.
 13. Process for installing aprestressed tensioning device for a traction means drive, whereby thetensioning device comprises: a tensioning arm (3) on which a tensioningroller (1) is rotatably mounted, a support (4) on which the tensioningarm (3) is pivotably arranged, a tension spring (8) which is supportedon the support (4) on one end and on the tensioning arm (3) on anotherend thereof, a stopper (12) which restricts a swiveling angle of thetensioning arm (3) and a detachable locking device (15) by which thetensioning arm (3), and the support (4) and the stopper (12) arelockable with one another, process comprising: locking the tensioningarm (3) and the support (4) and the stopper (12) with one another in anarrangement in which the tension spring (8) is prestressed, installingthe tensioning device in the traction means drive, partially releasingthe locking such that only the stopper (12) and the tensioning arm (3)are locked with each other by the locking device (15), whereby underforce of the prestressed tension spring (8), the tensioning arm (3) issprung against the traction means, fastening the stopper (12), andcomplete releasing of the locking such that the tensioning arm (3) isswivelable relative to the stopper (12).